There are circumstances where it is difficult to consistently choose TTL thresholds to perform the desired scoping. In particular it is impossible to configure overlapping scope regions as shown in figure 3.5, and there are a number of other problems with TTL scoping, and so more recently, administrative scoping has been added to the multicast forwarding code in mrouted[#!mrouted!#] and in most router implementations. Administrative scoping allows the configuration of a boundary by specifying a range of multicast addresses that will not be forwarded across that boundary in either direction.
